Synthesis of poly(diphenylacetylene)s bearing various polar groups and their gas permeability

Abstract

Diphenylacetylenes having a diisopropylphenoxysilyl, 2-bromoethoxy, trimethylsilyl and t-butyl groups (p-PhOSi(i-Pr)2C6H4C≡CC6H4-p-SiMe3 (1a), p-(BrCH2CH2O)C6H4C≡CC6H4-p-SiMe3 (1b), PhC≡CC6H4-p-SiMe3 (1c), PhC≡CC6H4-p-t-Bu (1d)) were polymerized to provide the corresponding poly(diphenylacetylene)s (2a–d). Treatment of the membrane of 2a with n-Bu4N+F− gave silanol-functionalized poly(diphenylacetylene) (3a). Fourier transform-infrared spectroscopy spectrum of 3a revealed that some silanol groups were consumed and the polymer was crosslinked via siloxane bond. The membrane of 3a exhibited very high gas permeability irrespective of the presence of polar silanol groups. Substitution of 1-methylimidazole to the membrane of 2b afforded an imidazolium salt-containing poly(diphenylacetylene) (3b (Br−)). Counteranions of 3b (Br−) could be exchanged by the treatment of the membrane with CF3COOK and (CF3SO2)2NLi, and membranes of 3b (TFAc−) and 3b (Tf2N−) were obtained. Introduction of 1-methylimidazole remarkably increased the selectivity (PCO2/PN2=31–44). The PCO2 values of 3b (Br−), 3b (TFAc−) and 3b (Tf2N−) were 11, 23 and 53 barrers, respectively, indicating that the CO2 permeability increased as the counteranion became bulkier. Polymers 2c and 2d were sulfonated using acetyl sulfate to give sulfonated poly(diphenylacetylene)s (3c and 3d). Polymer 3c exhibited high CO2 permselectivity, and the PCO2/PN2 was as large as 54. Polymer 3d with t-butyl groups showed relatively large PCO2 of 180 barrers and PCO2/PN2 of 30. Partially crosslinked poly(diphenylacetylene) (3a) bearing silanol groups were synthesized by the treatment of the membrane of 2a with n-Bu4N+F−. Imidazolium salt-containing poly(diphenylacetylene) (3b (Br−)) was obtained by the substitution of 1-methylimidazole to the membrane of 2b. Sulfonation of 2c gave a sulfonated poly(diphenylacetylene) (3c). The membrane of 3a was found to exhibit high gas permeability irrespective of the presence of the polar silanol groups in the polymer. Introduction of 1-methylimidazole into the membrane remarkably increased the CO2/N2 selectivity (PCO2/PN2=31–44). The sulfonated polymer 3c exhibited high CO2 permselectivity, and the PCO2/PN2 was as large as 54.